<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>NaN</title>
</head>
<body>
  <script>
  // console.log(NaN, typeof NaN)
  // console.log(0 / 0, 6 / 0, -6/0);
  // console.log(Math.sqrt(-1));
  // console.log("abc" - 10);
  // console.log(undefined + 5);
  // console.log(parseInt("hello"));
  const a = 0 / 0;
  const b = parseInt("hello");
  if(Number.isNaN(parseInt("hello"))) {
    console.log("不是一个数字, 不能继续计算了");
  }
  </script>
</body>
</html>